Conventionally, microelectromechanical systems (MEMS) microphones can be fabricated from a substrate, a backplate, and a flexible diaphragm, where the backplate, being in proximity to the flexible diaphragm, can form a variable capacitance device. In an aspect, a backplate can be perforated so that sound pressure entering the MEMS microphone package via a port can pass through the perforated backplate and deflect the diaphragm. In other implementations, sound pressure entering the MEMS microphone package via a port can directly impinge the diaphragm opposite the backplate. In such conventional MEMS microphones a direct current (DC) bias voltage (Vbias) applied to the backplate (or the diaphragm) facilitates measuring sound pressure induced deflections of the flexible diaphragm as an alternating current AC voltage, thereby providing a useful signal for further processing.
Note that, for a positive Vbias applied to the perforated backplate, where sound pressure passes through the perforated backplate to deflect the diaphragm, a positive going pressure wave traveling through the perforated backplate and deflecting the flexible diaphragm away from the perforated backplate will result in a decrease in the variable capacitance, which can result in a negative going output signal. In other words, a generated output signal appears inverted, 180 degrees out of phase, or of opposite polarity with the positive going pressure wave, which is not ideal in some cases.
In addition, some conventional MEMS microphone solutions may not be able to accurately sense very high sound pressure levels. As an example, the ability to accurately sense high sound pressure levels with a MEMS microphone can be limited by the distance between the diaphragm and the backplate, as well as the stiffness of the diaphragm, the designs of which, in turn, can be influenced by available Vbias at a microphone front end or operating voltage of an associated application specific integrated circuit (ASIC). However, for conventional bias voltage generator semiconductor circuits typically employed for such MEMS microphone front ends, voltage threshold levels of the semiconductor circuit limits available Vbias, while high voltage semiconductor circuitry can be expensive in terms of technology cost and die size, which can negatively impact sensor package size and costs.
It is thus desired to provide MEMS device bias voltage techniques that improve upon these and other deficiencies. The above-described deficiencies of MEMS microphones are merely intended to provide an overview of some of the problems of conventional implementations, and are not intended to be exhaustive. Other problems with conventional implementations and techniques and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.